Objectives: (1) To assess interactions and synergism of radiation with chemical agents; (2) To determine the effects of increased UV radiation from depletion of stratospheric ozone on skin carcinogenesis. Much of this program is devoted to the study of interactions of radiation with other environmental agents. To assess for interactions or synergism, groups of animals are exposed to radiation and chemicals alone or simultaneously, and maintained for their normal lifespan to compare the relative incidence and type of tumors induced. The lung cancer studies use particles of alpha-emitting Polonium-210 and/or Benzpyrene-hematite. The interaction of smoking and radiation is assessed by epidemiological and exfoliative cytology studies of uranium miners. Estrogenic hormones, and radiation (X and neutron) are used to study interactions in the induction of breast cancer. To assess the effects of depletion of stratospheric ozone on UV- induced skin carcinogenesis, an ozone chamber has been constructed to produce various thicknesses of ozone that filter the solar-simulated UV spectrum. Hairless mice are exposed to the UV radiation and maintained for the development of skin tumors. The results from these studies indicate that radiation acts synergistically with chemicals in inducing breast and lung cancer in animals. From the uranium-miner studies a similar relationship appears to exist in man.